Cathodoluminescent phosphors and methods for their fabrication are known in the art. They are employed in display devices, such as field emission displays, and are useful for forming the display image.
Prior art schemes for fabricating a phosphor within a display device include the step of forming a paste, which is applied to a substrate, such as by screen-printing. These pastes typically include a mixture of cathodoluminescent particles, organic dispersants, organic stabilizing agents, organic binders, inorganic binders, and a vehicle.
The organic dispersant is useful for controlling inter-particle forces within the phosphor paste. The inter-particle forces are controlled to provide a phosphor paste having favorable theological properties and favorable suspension stability. A low viscosity is preferred so that, for example, the thickness of the printed layer can be small. A thinner phosphor results in improved brightness when contrasted with a thicker phosphor. A lower viscosity also increases the upper limit of the particulate content, which defines a processable film.
The suspension stability refers to the tendency of the phosphor paste to maintain its suspension when it is allowed to sit. It is preferred that the phosphor paste have a high suspension stability so that the characteristics of the phosphor paste remain constant during the application process.
Such prior art schemes for fabricating phosphors, however, can result in undesirable effects when employed to fabricate field emission displays (FED's). First, the removal of organics from the printed phosphor paste requires combustion.
A typical substrate for an anode plate of a FED is made from soda lime glass, which has a temperature tolerance of about 500.degree. C. While the burnout temperatures of typical organic binders and organic stabilizing agents are below the temperature tolerance of soda lime glass, the burnout temperatures of typical organic dispersants, such as ammonium polyacrylates, are above the temperature tolerance of soda lime glass.
Thus, although removal of organics from the printed phosphor paste can be achieved by combustion, typically the removal is incomplete, resulting in residual carbonaceous residues in the phosphor. These carbonaceous residues can be liberated into the evacuated envelope of the FED.
The performance of a FED is sensitive to the presence of organic species within the evacuated region of the device. For example, the emissive properties of the electron emitters are adversely affected by the accumulation of organics at the surfaces of the electron emitters.
Furthermore, carbonaceous residues are believed to cause problems when dielectric spacer structures are employed. The dielectric spacer structures are useful for maintaining the separation distance between the anode and cathode plates of the FED. It is believed that the presence of carbonaceous residues at the surfaces of the dielectric spacer structures can result in the failure of the spacer during the operation of the FED. Thus, the presence of carbonaceous residue in prior art phosphors can have deleterious effects on the performance of a FED.
Accordingly, there exists a need for an improved phosphor and method for the fabrication thereof, which reduce or eliminate the need for organics and, in particular, organic dispersants in the phosphor paste.